He's not actually one of my professors he spoke to my class a couple nights ago though. He introduced himself by his first name, and seemed really cool and relaxed, didn't even know his last name til he wrote his email down. I went and talked with him after and he told me to send him an email, I'm just not sure if I should go as informal as what he introduced himself as, or if I should go for Dr. (lastname) as I don't really know him.